The research team led by Academy Research Fellow Heikki M. Tuononen has been able to identify the mechanism which enables some non-metal compounds to mimic the reactivity of their metal-based counterparts.
The research was conducted in collaboration with the research group of Dr. Warren Piers at the University of Calgary and the results have recently been published in the Journal of the American Chemical Society.
"These results could be dubbed a kind of "modern alchemy" in which chemical compounds are made to react in a way totally atypical to them. In alchemy, one of the main goals was to turn the less noble base metals into the more noble ones such as gold," says Dr. Tuononen.
The addition of molecular hydrogen to chemical compounds is one of the most widely used chemical reactions at the industrial scale, being particularly important for oil refinement and fertilizer industry. This reaction typically uses a metal-based catalyst to increase the reaction rate, as otherwise the breakup of the chemical bond in the hydrogen molecule (called activation) would require significant amount of energy. Since the catalysts used in the process are in general expensive (some are also toxic), there has been an ongoing effort to find cheaper and safer hydrogen-activation routes based on non-metal compounds.
"There are only a handful of non-metal compounds known which are able to activate molecular hydrogen in ambient conditions. So the boroles reported in 2010 by Dr. Piers were certainly a welcomed addition to the group! However, at that time, the mechanism of their metal-like reactivity could not be explained," tells Dr. Tuononen.
The research group of Dr. Tuononen specializes in theoretical modelling of chemical reactions at the molecular level. Concurrently with their computational studies, the group of Dr. Piers was conducting research on the unknown reaction mechanism using experimental techniques. At the end, the results from both investigations were combined, allowing for a detailed picture of the mechanism to be formed.
"The computational results were able to explain why these specific boroles react with molecular hydrogen in a seemingly similar manner to the traditional metal-based compounds even though they contain no metal atoms," describes postdoctoral researcher Virve Karttunen who is a member of Dr. Tuononen's research group. It was really spectacular that we were able to predict all the intermediates on the reaction pathway, one of which was also proven experimentally by the group of Dr. Piers.
The theoretical results obtained by Dr. Tuononen's research group show clearly that the reactivity observed for the boroles can be explained with their unique electronic structure. Although the investigated compounds will not function as new catalysts, the results fully support the idea that metal-like reactivity is possible for non-metal compounds and that we have just barely scratched the surface of this research area.
At the moment, researchers in my group are applying the theoretical data we have obtained thus far to design new non-metal compounds suitable for hydrogen activation. The collaboration with the group of Dr. Piers is also continuing active," tells Dr. Tuononen.
The project was funded by the Academy of Finland and the Technology Industries of Finland Centennial Foundation.
- Adrian Y. Houghton, Virve A. Karttunen, Cheng Fan, Warren E. Piers, Heikki M. Tuononen. Mechanistic Studies on the Metal-Free Activation of Dihydrogen by Antiaromatic Pentarylboroles. Journal of the American Chemical Society, 2013; 135 (2): 941 DOI: 10.1021/ja311842r
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